Plants represent a rich pool of bioactive compounds. Vanilla is one of those plants; it is used for the production of natural vanilla flavor. Besides its obvious flavoring capacity, it can also be used as an anti-oxidant and microbial agent. Vanilla extract is obtained from cured vanilla pods by ethanol extraction. Vanilla extract contains about 60 to 80 different flavor components, of which vanillin is the major flavor component. In the past several decades a number of patents, e.g., U.S. Pat. Nos. 4,874,701, 4,981,795, 2,195,871, 5,017,388, 5,262,315 and 5,128,253, and Japanese Patent Nos. 2,195,871 and 5,227,980, relate to the formation of vanilla flavors. These patents suggest various approaches using renewable, cheap and natural raw material sources such as ferulic acid, vanillic acid, vanillyl alcohol, eugenol, etc., employing either microorganisms, tissue cultures or enzymes, for vanillin formation.
Enzymes are widely used as a class of biocatalytic reagents in a wide variety of reactions including, e.g., oxidations, reductions, hydrolyses, and carbon-carbon bond ligations. Based on the nature of the solvent used, the enzymes can perform either a hydrolytic or a synthetic catalysis. Biocatalysts are valued for their intrinsic abilities to bind organic substrates and to catalyze specific and selective reactions under the mildest of reaction conditions. These selectivities and specificities are realized because of interactions occurring between the enzyme active site and the substrate molecule. Biocatalytic reactions are particularly useful when a traditional chemical catalysis is difficult and expensive to complete. Enzymes differ in their specificity towards substrates; some are highly selective while others accept a wide variety of substrates.
Selective reduction of aromatic acids to their corresponding aldehydes by Actinomycetes sp. was reported by Jezo and Zemek (1986). Enzymes such as aryl-aldehyde oxidoreductase (carboxylic acid reductase EC 1.2.1.30) catalyze the formation of vanillin from vanillic acid (Rosazza et al., 1998, U.S. Pat. No. 5,795,759). Cellulases (endoglucanase, cellobiohydrolase, cellobiase, beta-glucosidase, etc.) on the other hand hydrolyze the β-covalent bond between glucose units in cellulose chains.
The development of the vanilla flavor during the curing treatment is partly due to the hydrolysis of a glucosylated precursor. An example of such glycoside is vanillin glucoside, which occurs in green vanilla pods (Arana. F. E., 1943, Food Research, vol. 8, pages 343-351). Precise biochemical pathways leading to all flavor components of vanilla are not known. Many flavor compounds are bound in plants and microorganisms, simply to protect the cells against the toxicity of these compounds. An enzyme breaking the glycosidic bond releases the flavor compound from its bond. An example of this phenomenon is an enzyme β-glucosidase, which hydrolyses the β-covalent bond of glucose from an aglycone. Two patents (U.S. Pat. No. 5,705,205 and FR-A-2,634,979) focused on the green vanilla beans and their curing process, during which the flavor develops. Flavor enhancement and efficiency of the curing process was central to these to patents.
At the industrial level, vanilla extract is obtained from vanilla pods that have been successfully cured. U.S. Pat. No. 5,705,205 (1998) suggests usage of (β-glucosidase to shorten the curing process of green vanilla beans. Another patent FR-A-2,634,979 (1990) describes a process during which the green pods are frozen at a temperature of between −5 and 30 degrees C. and then reheated before extracting the flavor constituents therefrom. This process makes it possible to shorten the curing time and avoids losses of the flavor compounds which can occur during the curing process due to microbial or enzymatic decomposition. The typical curing process does not allow for the addition of external enzymes, only enzymes naturally present in the vanilla beans are employed in the curing process. Once the vanilla beans are cured the flavor compounds are extracted with ethanol. The remaining vanilla beans after the extraction are called spent or exhausted vanilla beans. These beans are typically used for animal feed and in very small quantities as food additives to give a visual impression of vanilla flavor, e.g., in vanilla ice cream. It is generally believed that most of the flavor is extracted during the extraction process and that these spent vanilla beans contain very minute amounts of flavor compounds.
Based on the forgoing background, it is an important object of the present invention to provide a process during which additional flavor compounds and food modifiers are released or transformed from complexes in spent vanilla pods, thereby obtaining additional vanilla flavors and food modifiers from the spent pods.